Grease Pencil objects
No this is not currently possible. There is some development happening with the grease pencil now so this may change in future versions.

After drawing a grease pencil stroke you can convert it to a curve object. This can be found in the grease pencil toolbar options.



This will convert the one active grease pencil layer to a curve object. The drawback is you loose any of the new fill settings and you need to bevel the curve and give it a material. Once you have the curve you can parent and duplicate as you want.

For the example you give I would draw a tree on an image and use the image as a texture on a plane.